Attentional inhibition or paracontrast?

In visual search experiments using asynchronous presentation of target and distractors, a robust and unexpected inhibition of reaction time was observed for the discrimination of a temporally trailing target. A number of experiments were required to determine the source of this inhibition. These experiments eliminated the possibilities that the inhibition might be a manifestation of three attentional processes: inhibition of return, attentional dwell time, or attentional capture by the temporally leading item.

Guided search: the effects of learning.

The previous report (Efron & Yund, 1996) offered an interpretation of the results of a number of search experiments within the theoretical context of the guided search model of Cave and Wolfe (1990) and Wolfe (1994). The present report extends this interpretation to the effects of extended practice when subjects search for a target defined by its orientation in the presence of a number of heterogeneous distractor items having differing orientations. Three experiments are described: The first revealed that over the course of 21 experimental sessions extending for a period of 6 weeks there were marked decreases in the magnitude of the reaction time gradient (RTG) and the right visual field superiority observed in the previous experiments.

Spatial nonuniformities in visual search.

Previous search experiments in this laboratory have been concerned with the marked differences in target detectability as a function of its location in the visual field-differences we have called a detectability gradient-when subjects were required to detect a vertically oriented "target" among a number of distractor items having different orientations. This gradient was characterized by a marked right visual field superiority as well as differences in the shape of the gradient in the two half fields. A scanning model was proposed to account for these robust phenomena.

Visual detectability gradients: effect of high-speed visual experience.

The detectability of a target pattern presented briefly with a number of similar nontarget patterns varies as a function of the spatial location of the target. Previous work attributes these detectability gradients to a visual search process--a non-eye movement serial scan--that examines a decaying neural representation of the image. (Heron, 1957; Efron, Yund, & Nichols, 1987, 1990a,b,c; Yund, Efron, & Nichols, 1990a,b,c).

Visual detectability gradients: effect of illiteracy.

When subjects are required to detect a target pattern presented simultaneously with a number of similar non-target patterns in a brief exposure, marked differences of target detectability are observed as a function of the spatial location of the target (Efron, Yund, & Nichols, 1987, 1990a, b, c; Yund, Efron & Nichols, 1990a, b, c). These differences in detectability as a function of retinal locus, referred to collectively as a "detectability gradient," have been attributed to a central serial processing mechanism, which scans the decaying neural representation of the image. There also is evidence suggesting that, at least in some circumstances, this gradient may be influenced by the direction in which subjects normally read (Heron, 1957; Mishkin & Forgays, 1952; Efron et al.

Detectability as a function of spatial location: effects of selective attention.

In a series of previous reports we have described differences in detectability of a target in a background of nontarget patterns as a function of its spatial location. These differences, referred to as a "detectability gradient," have been attributed to target detection accomplished by a serial processing mechanism--a scan. The mathematical model of such a mechanism, developed in the previous report, is equally applicable to a series of attentional shifts or to a perceptual, i.

Serial processing of visual spatial patterns in a search paradigm.

Previous experiments in this laboratory employing a search paradigm have found highly significant differences in the detectability of a briefly exposed target pattern as a function of the spatial location of the target when it is presented simultaneously with a number of discriminably different nontarget patterns. These detectability differences, at loci equidistant from the fovea, could not be accounted for by any known variation in retinal spatial resolution or by differential lateral masking effects of the target by nearby nontarget patterns. These observations led to the hypothesis that the target in these experiments was detected by a serial mechanism which "scanned" a persisting but rapidly degrading neural representation of the visual scene with increasing detection failures the later in time the scan processed the location occupied by the target.

Visual detectability gradients: the effect of distractors in contralateral field.

A number of studies involving recognition of tachistoscopically presented words have reported that the typical right visual field performance superiority associated with linguistic stimuli is enhanced by bilateral presentations (simultaneous stimuli in both visual half-fields) compared to unilateral presentations (stimuli in only one half-field on a trial). We have reported the same phenomenon, however, using visual spatial patterns in a search paradigm (E. W.

Target detection in one visual field in the presence or absence of stimuli in the contralateral field by right- and left-handed subjects.

Marked differences in detectability are observed as a function of retinal locus when subjects are required to find a briefly exposed target pattern of uncertain location in the presence of a number of discriminably different nontarget patterns. Our previous studies using this search paradigm have attributed these detectability differences, and the right visual field detectability superiority associated with them, to a serial (scanning) mechanism which tends to examine stimuli in the right field earlier than those in the left. The present experiment, performed on large groups of right- and left-handed subjects, was designed to test the hypothesis that there are two independent serial processors, one in each hemisphere--an hypothesis which might account for the differences in detectability within and between the two half-fields in terms of hemispheric processing differences.

Detectability as a function of target location: effects of spatial configuration.

Marked differences in detectability as a function of spatial location, a "detectability gradient," are observed when subjects are required to detect a briefly exposed target pattern of uncertain location in the presence of a number of nontarget patterns. Target detectability also is inversely related to the number of nontarget patterns which are present in this search paradigm. These previous findings provide strong evidence for a serial process in which increasing probability of error occurs during a scan of a rapidly degrading neural representation of the visual image following a brief exposure to the stimuli.

Detectability gradients as a function of target location.

We examined the ability to detect a specified visual pattern (a target) in a randomly selected location when it was briefly presented with 11 other spatially distributed nontarget patterns and also when it was presented by itself for the same duration (50 msec) on a background of visual noise. Two experiments were designed to measure target detectability as a function of its location in the visual field where all possible target locations were equidistant from the fovea. A right visual field detection superiority was obtained in both experiments.

Scanning the visual field without eye movements--a sex difference.

Subjects identified the location of a briefly exposed target pattern in the presence of five other patterns. Right-handed females, but not males, exhibited a significantly higher error rate in correctly localizing the target pattern when it was in the left visual field, particularly for the left parafoveal region. This unexpected distribution of errors as a function of target location can be accounted for by a sequential (serial) mechanism which scans the visual field.

Speech discrimination with an 8-channel compression hearing aid and conventional aids in background of speech-band noise.

The design for a multichannel compression hearing aid was developed from previous experimental and theoretical work in our laboratory concerning pitch perception in normal-hearing subjects. The new hearing aid, implemented with off-line digital signal processing, was tested on twenty subjects with sensorineural hearing loss using speech sounds in a background of speech-spectrum noise. Five signal-to-noise ratios (+15 to -5dB) were used at two noise levels (60 and 70 dB SPL).

Phenytoin increases the severity of cortical hemiplegia in rats.

The effects of systemic phenytoin administration on the motor deficit resulting from a cortical lesion were studied in rats trained to walk coordinately on a narrow beam. The somatomotor cortex lesion was produced by an indwelling cannula through which saline or GABA were infused chronically via an osmotic minipump. Phenytoin (50 mg/kg i.

Hemispheric specialization of memory for visual hierarchical stimuli.

Unilateral brain-damaged patients and normal control subjects were asked to remember visual hierarchical stimuli consisting of larger forms constructed from smaller forms. The right-hemisphere damaged patients made more errors in remembering the larger forms relative to the smaller forms, whereas the left-hemisphere damaged patients made more errors in remembering the smaller forms relative to the larger forms. These findings are discussed as they relate to hemispheric specialization for visuospatial processing.

An ear asymmetry for gap detection following anterior temporal lobectomy.

A threshold elevation in the performance of auditory temporal order judgment in man has been reported in the ear contralateral to the side of an anterior temporal lobectomy. On the basis of temporal order judgments alone it is not possible to determine whether the deficit is attributable to an impairment of recognition, identification, or temporal resolution. The present monaural experiments compared the performance of the two ears in the detection of a gap in a broad-band noise burst in normal and temporal lobectomized subjects.

Central auditory processing. VI. Detecting ear dominance by evoked potentials.

An electrophysiological method is described for measuring the direction and strength of a subject's ear dominance for pitch using the P3 component of event-related potentials. Results of these experiments reveal that the P3 can be used effectively for these measures in man.

Central auditory processing. IV. Ear dominance--spatial and temporal complexity.

Ear dominance for dichotically presented tones was measured in 63 righthanded subjects when the frequency difference (delta f) was small compared to the center frequency (fc) and again when it was large. Although two-thirds of the population exhibited a left-ear dominance in both conditions, a shift toward right-ear dominance occurred when the delta f was increased. An additional study, employing the alternating tone illusion described by Deutsch, revealed the same general effect, i.

Central auditory processing. III. The "cocktail party" effect and anterior temporal lobectomy.

The capacity to selectively attend to only one of multiple, spatially separated. simultaneous sound sources--the "cocktail party" effect--was evaluated in normal subjects and in those with anterior temporal lobectomy using common environmental sounds. A significant deficit in this capacity was observed for those stimuli located on the side of space contralateral to the lobectomy, a finding consistent with the hypothesis that within each anterior temporal lobe is a mechanism that is normally capable of enhancing the perceptual salience of one acoustic stimulus on the opposite side of space, when other sound sources are present on that side.

Central auditory processing. II. Effects of anterior temporal lobectomy.

Ear dominance for the pitch of dichotically presented tonal stimuli was measured in nine patients before and after a unilateral anterior temporal lobectomy. Four subjects had a left and five had a right lobectomy. Every patient exhibited a change of ear dominance consistent with the hypothesis that a unilateral lobectomy decreases the perceptual salience of the tone presented to the ear contralateral to the lesion.

Central auditory processing. I. Ear dominance--a perceptual or an attentional asymmetry?

The phenomenon of ear dominance for pitch described by Efron and Yund has been attributed by them to an asymmetry of sensory origin in the binaural integration of dichotic tone pairs. An explanation of this phenomenon in terms of an attentional bias is rejected on the basis of two experiments where the possibility of such bias was excluded. These and other experiments indicate that a simple explanation of this ear dominance in terms of a hemispheric specialization in the processing of tonal stimuli also must be rejected.

Individual differences in the perception of dichotic chords.

A new method was employed to measure the changes in the strength of ear dominance in the perception of dichotic chords as a function of stimulus intensity. The results of the first experiment, where the right and left tones were of equal intensity, revealed striking individual differences in the way the ear dominance of five subjects changed as the intensity of the chords was varied over a 60-dB range--no two subjects exhibiting the same pattern of behavior. Since, within the context of the model of Yund and Efron [J.